This patent application claims priority to Japanese Patent Application No. 8-305510, filed Nov. 1, 1996, which is incorporated herein by reference.
1. Field of Invention
The present invention pertains to a composite material made of a low-density polyethylene and a lamellar silicate, and it further pertains to a composite material with high transparency achieved through the thorough dispersing of a lamellar silicate with a low-density polyethylene produced by inserting a low-density polyethylene between the silicate layers of a lamellar silicate. A film made of the low-density polyethylene-lamellar silicate composite material of the present invention is transparent and has excellent gas-barrier properties, and an injection molding made thereof has greater rigidity while maintaining a glossy surface, and is used effectively for moldings that require both a high-gloss surface and rigidity such as bumpers for vehicles and OA machines.
2. Background
In the past, many attempts have been made to produce a composite material by inserting an organic polymer material between silicate layers that comprise a lamellar silicate. That research is summarized in Chuzo Kato (Polymers, 1970, Vol. 19, No. 222, pp. 758-764), and Chuzo Kato and Kazuyuki Kuroda (Clay Science, 1986, Vol. 26, No. 4, pp. 292-305), etc. However, it has not been possible to increase the distance between layers through insertion of an organic polymer material between the silicate layers or dispersion of a clay mineral, even when the parallelism between layers is reduced.
As a composite material developed to eliminate the above-mentioned problem, a clay mineral/polyamide resin composition produced by polymerization of the silicate layer that forms an expandable clay mineral with an alkylamine expanding agent after performing treatment, as needed, and further impregnating with a monomer is known (Japanese Kokai Patent Application Nos. Sho 58[1983]-35211 and Sho 58[1983]-35542). Also, a composite material produced by mixing a resin containing a polyamide with a silicate layer having a thickness of the silicate layer that forms the lamellar silicate in the range of 7-12 .ANG. (angstroms) and a layer to layer distance of at least 30 .ANG. has been reported (Japanese Kokai Patent Application No. Sho 62[1987]-74957). In manufacturing the above-mentioned composite materials, a polymerization reaction is included in the production process; thus, production is not necessarily easy.
As a material that can be produced without difficulty in the production process, a resin composition containing a composite material produced by hot-melt kneading of a lamellar silicate/alkylamine expanded composite material prepared by first dispersing a low-density polyethylene and an alkylamine expansion agent with a polyamide to increase the distance between layers to at least 30 .ANG. and to reduce the parallelism between layers has been reported (U.S. Pat. No. 5,385,776).
Furthermore, the applicant has developed a method for manufacturing a composite material consisting of dispersing mixing, drying and pulverizing a polar organic polymer material that can be dissolved or dispersed in water and can be hot-melt mixed with a lamellar silicate in order to produce a composite material having good thermostability that can be easily produced and is capable of dispersing a lamellar silicate even when an organic polymer material other than polyamide is used (Japanese Patent Application No. Hei 8[1996]-65355).
As shown, the above-mentioned technologies concern composite materials produced by dispersing a lamellar silicate in a polymer having a polar group in an organic polymer such as a polyamide and an ionomer, and the focus is on composite materials made primarily of a polar polymer. In this case, the low-density polyethylene includes a polar group, thus, affinity with nonpolar polymers is inadequate, and adequate dispersion cannot be achieved; as a result, transparency is lost.
However, in recent years, studies on dispersing a lamellar silicate in a nonpolar polymer have been carried out. For example, as a method for manufacturing a composite material consisting of dispersing montmorillionite in a polymer, a method in which ion-exchange treatment is performed for a sodium montmorillonite with distearyldimetylammonium in water, followed by washing, pulverization and drying to produce an organic montmorillonite, a reaction is performed with an oligomer in an organic solvent having affinity for both the polymer and the montmorillonite, followed by washing and drying, and hot-melt kneading is carried out for the polymer has been reported (Fall of 1995, Polymer Processing Technology Discussion Meeting, Lecture Material, pp. 53-54, Synthesis and Properties of PP Clay Hydrides).
Excellent dispersively can be achieved in the above-mentioned method, but the method involves many steps in the production process and is complex and not practical.
Furthermore, a composite material produced by dispersing a lamellar silicate with a low-density polyethylene used for films, etc. because of softness and transparency and having good processability using a very simple method has not been developed.
3. Problems to be Solved by the Invention
Based on the above background, the objective of the present invention is to produce a composite material by dispersing a lamellar silicate in a low-density polyethylene, which is a type of nonpolar polymer, and to provide a simple method for manufacturing thereof.